Use of nonionic esters in a coating for surfaces coming in contact with blood

ABSTRACT

The present invention relates to methods for coating at least one surface of a medical device for improving the hemocompatibility of said surface. Further, the invention relates to medical devices comprising surfaces, coated with a coating composition containing a nonionic ester formed from an acyclic C 3 -C 6 (OH) 3-6  polyol and from at least three C 12 -C 26  fatty acids, and further includes at least one hydrophilic group.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of international patent applicationPCT/EP 2006/007867 filed on Aug. 9, 2006 and designating the U.S., whichwas published in German as WO/2007/0199940 and claims priority of Germanpatent application DE 10 2005 040 211.9 filed on Aug. 16, 2005. Theentire contents of these priority applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to the use of at least one nonionic esterin a coating for surfaces which come into contact with blood to improvethe hemocompatibility of the surfaces.

The invention further relates to a medical device having at least onesurface which has a coating in which a nonionic ester is used.

RELATED PRIOR ART

Various coating compositions and methods for coating medical devices areknown in the state of the art.

Plastics surfaces which come into contact with a patient's blood overlonger or shorter periods are used in many medical treatments. Devicesof this type are for example disposable equipment for a heart-lungmachine, oxygenators, catheters, artificial organs such as heart orkidney, gas exchange membranes or vascular prostheses, but this list isby no means to be regarded as a conclusive list.

With these plastics surfaces it is extremely important inter alia toprevent the blood which comes into contact with the surfaces fromcoagulating, and overall to make the surface hemocompatible.

It is known in this connection for example to inhibit blood coagulationby giving a high dose of heparin or else to bind heparin to thosesurfaces coming into contact with blood.

It is further known in the state of the art to coat surfaces withhydrophilic polymers or surfactants such as, for example, Pluronic™which, it has been possible to show, improves the hemocompatibility ofsurfaces which come into contact with blood. Thus, for example, U.S.Pat. No. 6,670,199 describes various coatings which include Pluronic™ asbasic structure which can be conjugated with various biomolecules.

Experiments on the applicant's premises have now shown that although theabovementioned coatings have antithrombogenic properties, they also atthe same time showed a large deterioration in complement activation. Theknown coatings therefore do not comply in this regard with what isunderstood by good compatibility with blood.

Good compatibility with blood (=hemocompatibility) of a surface meansspecifically that on contact with blood it initiates neither bloodcoagulation nor the defense mechanisms of the body against the foreignsurface.

The high complement activation which is surprisingly found with theknown coating with Pluronic™ is precisely disadvantageous in particularbecause it may lead to systemic inflammations and for example causepostoperative organ failure.

Also described in the prior art are coatings with hemocompatiblepolymers. However, a precondition therefor is the use of suitableorganic solvents. The plastics to be coated may, however, be attacked bythese solvents in an unacceptable manner, thus possibly impairing thefunctioning of the devices. Polymers of lower molecular weight butsufficient solubility to be able to be delivered from aqueous media showa greater tendency to be washed away from the surface by theblood-stream.

SUMMARY OF THE INVENTION

Against this background, it is an object of the present invention toprovide alternative substances which can be used for coating surfaceswhich come into contact with blood in order to improve thehemocompatibility of surfaces coated in this way, and which can beapplied from aqueous media as solution or emulsion in a simple process,but nevertheless show sufficient adhesion in order not to be washed awayby the blood stream.

According to one aspect of the invention, there is provided a non-ionicester, where the nonionic ester is formed from an acyclic C₃-C₆(OH)₃₋₆polyol and from at least three C₁₂-C₂₆ fatty acids, and where thenonionic ester further includes at least one hydrophilic group.

This is because the inventors of the present application have found thatthe hemocompatibility of surfaces which come into contact with blood isimproved overall through the use of said nonionic esters. Compared withsurfaces coated with Pluronic™, it has been possible in particular toachieve great improvements in relation to complement activation.

The inventors have for example subjected various substances which have abasic structure defined according to the invention to tests ofhemocompatibility both in the HLM (heart-lung machine) in vitro test andin the Chandler loop test. With the novel coating it was possible toachieve, inter alia in the test for the number and activation of bloodplatelets (β-thromboglobulin), a marked improvement in thehemocompatibility compared with uncoated surfaces and surfaces coatedwith Pluronic™.

A further advantage over previously disclosed coatings is that anoptimal adhesion of the coating to the surface which comes into contactwith blood can be achieved with the newly provided substances. Goodadhesion of the coating to the surface is particularly importantbecause, on the one hand, substances which adhere inadequately may enterthe bloodstream and may then possibly induce side effects in thepatient. On the other hand, there is in turn the risk with coatingswhich adhere inadequately and are washed away by the bloodstream thatthe surface no longer has sufficient hemocompatibility and—besides theside effects induced by the released coating substance—there may be forexample additionally activation of blood components through contact withthe exposed surface.

With the coating substance which is provided for the first time herein,i.e. the nonionic ester, the at least 3 fatty acids ensure that thesubstance firmly adheres to the surface, or is anchored to the surface.Disadvantageous washing away with the possible consequences describedabove is thus successfully avoided.

In addition, the hydrophilic portion of the nonionic ester ensures theantithrombogenic property of the coating and thus its goodhemocompatibility.

In a preferred embodiment, the hydrophilic group of the ester can beselected from the group comprising hydroxyl, methoxyl, ethoxyl andethoxylate, homopolymers of vinyl compounds and copolymers of vinylcompounds. In a further refinement it is preferred for the vinylcompound to be selected from the group comprising vinylpyrrolidone,acrylamide, acrylic ester, methacrylic ester.

The inventors of the present application have realized that thehydrophilic group of the ester can be selected from the groupsmentioned, because the listed groups are sufficiently hydrophilic, whichis important overall for optimal hemocompatibility. As already mentionedabove, the acyclic polyol forms in this case with the fatty acids ananchor via which the substance can adhere durably to the surface. Thehydrophilic groups ensure the antithrombogenic effect of the coating.

In yet another refinement of the invention, the hydrophilic group isconnected via the polyol to the nonionic ester.

Thus, in this embodiment, the at least one hydrophilic group is linkedvia the C₃-C₆(OH)₃₋₆ polyol to the ester. While at the same timeensuring the stable anchoring of the coating to the surface, in turn anadequate hydrophilic property of the coating is at the same timeprovided thereby.

It is preferred in another embodiment of the invention for thehydrophilic group to be connected via the fatty acid to the ester.

This embodiment also provides the advantages of a firm anchoring of thecoating to the surface with, at the same time, good hydrophilicproperties. In this case too, the acyclic polyol and the fatty acidsprovide a stable anchoring, whereas in turn the hydrophilic portion,which in this case is connected via the fatty acids to the ester,provides optimal hemocompatibility. In this embodiment for example thesubstance used according to the invention includes fatty acids of whichat least one has an ethoxylated hydroxyl group.

It is preferred in a further embodiment for the nonionic ester to have aformula which is selected from the following formulae:

a)

in which

R1-3 is in each case a C12-C26 fatty acid which are identical ordifferent, saturated or unsaturated, and which have where appropriate atleast one hydroxyl group,

n is an integer from 1 to 4, and

a-f are integers which may be identical or different, where the total ofthe numbers a-f is between 0 and 200;

b)

in which

R1-3 is in each case a C12-C26 fatty acid which are identical ordifferent, and saturated or unsaturated, where at least one of theradicals₁₋₃ has at least one hydroxyl group,

n is an integer from 1 to 4,

a-f are integers which may be identical or different, where the total ofthe numbers a-f is between 0 to 200;

c)

in which

R1-3 is in each case a C12-C26 fatty acid which are identical ordifferent, and saturated or unsaturated, where at least one hydrophilicradical from homo- or copolymers of vinyl compounds is linked to atleast one of the radicals R1-3,

n is an integer from 1 to 4.

It will be appreciated that, during the synthesis of the compound, theat least one hydrophilic radical will be linked to the radicals R1-3 viaat least one double bond thereof.

All the alternatives mentioned provide, because of the common basicstructure, the advantage that stable anchoring of the substance to thesurface, and a hydrophilic property sufficient for goodhemocompatibility is ensured.

The inventors have been able to show in their own experiments that asubstance used according to the invention, specifically Cremophor ELwhich is used in the state of the art as solubilizer/emulsifier, confersan excellent hemocompatibility on the surfaces coated therewith.Cremophor represents in this connection one example of an ethoxylatednonionic ester of acyclic polyol with fatty acids. Said substance hasbeen tested for example for the platelet count and activation(β-thromboglobulin) etc compared with substances known in the state ofthe art.

The inventors were able to infer from these experiments that sub-stancesof similar structure are likewise suitable for an optimal hemocompatiblecoating. It is preferred in a further embodiment for the nonionic esterto have a formula which is selected from the following formulae:

a)

in which

R1-4 is in each case a C12-C26 fatty acid which are identical ordifferent, saturated or unsaturated, and which have where appropriate atleast one hydroxyl group, and

a-d are integers which may be identical or different, where the total ofthe numbers a-d is between 0 and 200;

b)

in which

R1-4 is in each case a C₁₂-C₂₆ fatty acid which are identical ordifferent, saturated or unsaturated, where at least one of the radicalsR₁₋₄ has at least one hydroxyl group,

and

a-d are integers which may be identical or different, where the total ofthe numbers a-d is between 0 and 200;

c)

in which

R1-4 is in each case a C12-C26 fatty acid which are identical ordifferent, saturated or unsaturated, where at least one hydrophilicradical from homo- or copolymers of vinyl compounds is linked to atleast one of the radicals R1-4.

It will be appreciated here too that, during the synthesis of thecompound, the at least one hydrophilic radical will be linked to theradicals R1-3 via at least one double bond thereof.

With these compounds, which represent branched molecules based onpentaerythritol, it is possible to achieve a hemocompatible property ofcoatings which is just as good as that of the abovementioned unbranchedmolecules. Fatty acid esters of pentaerythritol are employed in thestate of the art inter alia as emulsifiers.

In a refinement it is preferred for the nonionic ester to have an HLB(HLB=hydrophilic-lipophilic balance) of between 2 and 18, preferablybetween 4 and 14.

The HLB describes the ratio between hydrophilic and lipophilic portionsof a chemical compound. The inventors have found that it is possible byadjusting the HLB to the stated values to provide a substance whichconfers on the coating an optimally adapted hydrophilic property.

It is preferred in a further embodiment for the nonionic ester to beselected from the group comprising polyoxylglycerol ricinoleate,polyoxylglycerol hydroxystearate, polyoxylsorbitol hexaoleate.

These compounds have been proved in experiments to be suitable forcoating within the meaning of the present application. One example ofpolyoxylglycerol ricinoleate (synonym: macrogol-glycerol ricinoleate) isCremophor® EL, one example of polyoxylglycerol hydroxystearate (synonym:macrogol-glycerol hydroxystearate) is Cremophor® WO 7, and one exampleof polyoxylsorbitol hexaoleate (synonym: macrogol-sorbitol hexaoleate)is Atlas® G 1086 or Atlas® G 1096. Said substances are commerciallyavailable on the market.

The enumerations are only by way of example, because it is possible toemploy all conceivable substances having a structure according to theinvention.

In yet another refinement it is preferred for the coating solution forthe hemocompatible coating to consist of an aqueous solution or emulsionwhich comprises the nonionic ester.

In a further refinement it is preferred for the nonionic ester contentin the aqueous solution or emulsion to be less than 2% by weight,preferably less than 0.2% by weight.

The inventors of the present application have realized that theseproportions of the nonionic ester in the solution are sufficient to leadto a marked improvement in the hemocompatible properties.

Against this background, the present invention further relates to ahemocompatible coating for surfaces which come into contact with blood,in which at least one nonionic ester as defined above is applied.

It is thus possible—as already mentioned—to use the hemocompatiblecoating to coat surfaces of, for example, medical devices which comeinto contact with blood, and with which it is extremely important thatthey acquire good hemocompatible properties. This results in preventionof, for example, activation of the complement system in blood, or forexample adsorption or activation of blood platelets or white bloodcorpuscles.

Against this background, the present invention further relates to amedical device having at least one surface which has the hemocompatiblecoating according to the invention. The surface of the medical device ispreferably a plastics surface, in particular composed of polypropylene,polycarbonate, polymethylpentene, polyurethane, polyethylene, polyester,silicone, rigid or plasticized polyvinyl chloride, copolymers such as,for example, ABS, EPDM etc.

In a refinement it is preferred for the medical device to be a componentof a device coming into contact with blood, preferably of disposableequipment for a heart-lung machine, an oxygenator, a catheter, anartificial heart, an artificial kidney, a gas exchange membrane or avascular prosthesis.

It will be appreciated that the features mentioned above and yet to beexplained below can be used not only in the combinations indicated ineach case, but also in other combinations or alone, without departingfrom the scope of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Further advantages are evident from the appended description and thetable.

TABLE 1 Results of the Chandler loop tests Pluronic Cremophor ControlUncoated F68 EL Blood platelets × 10³/μl 264 187 225 249 β-TG 72.21601.0 1760.9 809.0 IU/ml SC5b-9 ng/ml 156.3 1864.7 7577 3148

Table 1 shows results for test specimens with various coatings subjectedto a test in the Chandler loop model. This entails tubes (loops) partlyfilled with blood and having various coatings being rotated in awaterbath. This results in the “blood column” and the tube rotatesaround the blood column and simulates a flow. After 90 minutes, bloodwas taken from the loops, and these samples were analyzed for certainvalues.

The specimens (loops) in the tests carried out in the present caseconsisted of 7 commercially available polycarbonate connectors whichwere connected by ⅜″ silicone tube pieces to form a ring.

In each case 5 of such loops were assembled for the coating, and 1000 mlof aqueous coating solution was circulated using 1 m of ⅜″ silicone pumptube by pumping with a tubing pump at a flow rate of two liters perminute for 20 minutes at room temperature. After the coating, thecoating solution was discarded and the coated loops were, withoutfurther rinsing, blown out with sterile compressed air and thus dried.After a final drying in a drying oven at 40° C. for four hours, thecoating process was complete. The coating solutions used had thefollowing compositions: coating A: 1000 mg/liter Cremophor®EL(Caesar+Loretz GmbH, Hilden) in demineralized water; coating B: 1000mg/liter Pluronic®F68 (AppliChem GmbH, Darmstadt) in demineralizedwater.

Table 1 lists the number of blood platelets after carrying out the testfor each tested tube. It is evident from the table that the number ofblood platelets is slightly higher with the Cremophor coating than withthe Pluronic coating, but is distinctly higher than with the uncoatedcontrol.

Table 1 additionally shows the result of the β-thromboglobulindetermination (quantitative, IU/ml). β-Thromboglobulin is released onactivation of blood platelets, so that the β-thromboglobulinconcentration is a measure of the activation of blood platelets.

As is evident from Table 1, the Cremophor coating leads to a distinctlysmaller release of β-thromboglobulin than the surface coated withPluronic™ and the uncoated surface.

Table 1 additionally shows the result of the complement SC5b-9determination (nanograms/ml). The terminal complement complex is arelevant marker for evaluating the hemocompatibility of surfaces. SC5b-9has the ability to attack cell membranes and, for example, to activateblood platelets. It must therefore be the aim with every coating tominimize the formation of this complement complex.

The comparison between Pluronic™ and Cremophor in Table 1 again revealsthat Cremophor leads to a far lower SC5b-9 value than does Pluronic®F68(about 3000 ng/ml for Cremophor compared with about 7600 ng/ml forPluronic; averages in each case).

The results in the Chandler loop show that the coating according to theinvention has better hemocompatible properties than the specified priorart coating.

1. A medical device having at least one surface intended to come intocontact with blood, said at least one surface having a coatingconsisting of polyoxylglycerol ricinoleate which adheres the coatingdirectly to the at least one surface of the medical device.
 2. A medicaldevice having at least one surface intended to come into contact withblood, said at least one surface having a coating comprisingpolyoxylglycerol ricinoleate which adheres the coating directly to theat least one surface of the medical device.
 3. The medical device ofclaim 1, wherein said surface is a plastics surface.
 4. The medicaldevice of claim 1, wherein said surface consists of at least one of thematerials polypropylene (PP), polycarbonate (PC), polymethylpentene(PMP), polyurethane (PU), polyester (PE), silicone, polyvinyl chloride(PVC), acrylonitrile butadiene styrene (ABS), and ethylene propylenediene monomer (EPDM).
 5. The medical device of claim 1, wherein themedical device is selected from the group consisting of disposableequipment for a heart-lung machine, an oxygenator, a catheter, anartificial heart, an artificial kidney, a gas exchange membrane or avascular prosthesis.
 6. The medical device of claim 2, wherein saidsurface is a plastics surface.
 7. The medical device of claim 2, whereinsaid surface consists of at least one of the materials polypropylene(PP), polycarbonate (PC), polymethylpentene (PMP), polyurethane (PU),polyester (PE), silicone, polyvinyl chloride (PVC), acrylonitrilebutadiene styrene (ABS), and ethylene propylene diene monomer (EPDM). 8.The medical device of claim 2, wherein the medical device is selectedfrom the group consisting of disposable equipment for a heart-lungmachine, an oxygenator, a catheter, an artificial heart, an artificialkidney, a gas exchange membrane or a vascular prosthesis.